Conventionally, it is known that a drive transmission mechanism using a timing belt used in an electrophotographic image forming apparatus is mostly used in a part which does not comparatively influence upon images such as discharged paper feeders because a speed noticeably varies in one cyclic frequency of the belt. Therefore, it is known that a transmission mechanism in which gears are arrayed is used for an image forming drive transmission mechanism particularly likely to influence upon images among drive mechanisms.
Japanese published unexamined application No. 2004-100863 discloses an image forming apparatus using a timing belt and preventing a rotational shift variation thereof.
Japanese published unexamined application No. 2001-254790 discloses a configuration of dividing a timing belt into two and shifting the two belts at n/2 teeth when assembled to counteract eccentric components thereof each other for the purpose of preventing synchronized rotational shifts due to the eccentric components.
However, a conventional drive transmission mechanism using only a gear needs to use many gears when there is a distance between a drive member and a driven member and possibly deteriorates in banding due to overlapping of speed variation in engaging frequency or shock jitter due to the many gears therebetween. In order to solve this problem, precision gears have to inevitably be used and members holding the gears need to precisely be processed, resulting in higher cost of the drive mechanism. Therefore, precise drive using a timing belt has been studied, but a displacement of one cyclic component of the belt noticeably influences upon images. Further, when the belt has a maximum or a minimum length, speed variation noticeably deteriorates.
In Japanese published unexamined application No. 2004-100863, a pair of timing belts are hung around a drive pulley and a driven pulley with tension, and which cannot be used in the present invention having a relay member.
In Japanese published unexamined application No. 2001-254790, the two belts counteract the eccentric components thereof each other. However, variation components deteriorate according to the maximum or the minimum quality, and forming the two belts at the same position costs, which leaves room for improvement.
Because of these reasons, a need exists for a low-cost synchronized drive unit preventing speed and positional variation of one cyclic component of a timing belt in an image forming apparatus using the belt as a drive transmission mechanism.